build: don't try to `ls -lh` executables that don't exist

Avoids `ls: cannot access build/debug/node_g: No such file or directory`.
Not an actual error but it confuses people.

Makefile

@@ -11,8 +11,8 @@ web_root = ryan@nodejs.org:~/web/nodejs.org/
 export NODE_MAKE := $(MAKE)
 
 all: program
-	@-ls -lh build/default/node
+	@-[ -f build/default/node ] && ls -lh build/default/node
-	@-ls -lh build/debug/node_g || echo ""
+	@-[ -f build/debug/node_g ] && ls -lh build/debug/node_g
 
 all-progress:
 	@$(WAF) -p build